1. Field of the Invention
This invention relates to gas laser tubes and more particularly to those laser systems operating in a pulse mode at high pressure.
2. Description of the Prior Art
One of the sources for high average power laser output is the high pressure transversely excited laser. A typical arrangement for such a laser provides for two long electrodes (one often including a number of pin cathodes and the other being a continuous anode) a few centimeters wide and spaced a few centimeters apart. The optical axis of the laser is parallel to the electrode surfaces and transverse to the electric field established between the electrodes. The lasing gas is circulated through the electrode gap in a direction transverse both to the optical axis and the electric field at typical velocities in the range of 15 m/sec to 120 m/sec.
In such lasers, population inversion is obtained by a pulsed glow discharge generated by applying a pulsed voltage across the electrode gap. Complete breakdown of the gap when the pulse is applied must be avoided to have proper laser operation. By tailoring the duration and shape of the pulses to avoid overheating of the gas the chance of complete breakdown can be reduced although the most efficient lasing conditions may not be achieved since the value of E/N cannot then be independently optimized.
One reason for breakdown in prior laser configurations has been lack of control over the ratio of electric field strength to the density of gas molecules (E/N) in the region where exciting collisions occur. The field, to obtain efficient ionization of the gas, must be high while optimum excitation conditions require a reduced value of E/N. If ionization and excitation occur in the same or overlapping regions, optimum conditions for both ionization and excitation cannot be acheived.
One method of separating the ionization and excitation regions in a low pressure CW laser is by utilizing a coaxial electrode configuration. Such a configuration is operative for low voltage D.C., static gas, and low pressure conditions. Under high voltage and high pressure conditions, however, overheating of the gas would occur and breakdown of the gap would result since no allowance is made for gas flow.